1. Field of the Invention
This invention relates to electromagnetic shields, in particular ones that are used to shield contactless smart cards or RFID microchips and prevent unwanted wireless exchange of data between the card or chip and a remote transceiver (reader).
2. Description of Prior Art
Contactless “smart cards” (smart because they contain an embedded electronic computation device, also called an electronic computation means) are able to store a relatively large amount of data on an imbedded microchip. Unlike magnetic strip cards such as the conventional credit card, and contact smartcards with exposed electronic contacts for communicating with the embedded electronic computation device, contactless smart cards can exchange information with a “reader,” via electromagnetic energy transfer such as magnetic, RF, infrared radiation or light without coming into physical contact with the reader. The inductive coupling between the reader and the card is used to transfer both the energy necessary to energize the embedded electronic storage device and the electronic data that may be stored in the embedded electronic device or devices. The electrical signal transfer is based on a technique that can be described as a loosely coupled transformer means. A strong, high-frequency magnetic field is typically generated by a coil in the reader in order to transfer the energy and data to and from the embedded electronic device or devices.
When a contactless smart card is brought into the vicinity of the reader, a portion of the reader's magnetic field passes through an antenna (typically a coil) in the card induces a voltage in the antenna, and initiates current flow. This is the typical mechanism for the energy transfer between the reader and the card without direct physical contact between the reader and the card. Information on the card is then “broadcast” back to the reader by the embedded electronic device or devices in the card through a broadcast means built into the card.
The use of the contactless card technology enables convenient, quick exchange of information stored on the embedded electronic means in the in card. However, due to the convenient contactless information transfer feature, the card can be susceptible to unwanted information transmission to an unauthorized receiver that appropriately excites the embedded electronic means. In addition, if the card is energized by an undesired or unauthorized reading means (aka “snooping”), and a data transfer initiated, the person carrying the card has no knowledge of the card's unauthorized access and transmission. Interrogation can occur regardless of where on his person the individual is carrying the card. Encryption and other security features and communication protocols are currently used to help protect the integrity of the card information and its signal, but another layer of physical protection means is beneficial.
The chips used in smartcards can also be manufactured in a less sophisticated form called a Radio Frequency Identification (RFID) chip. These chips come in several different embodiments for various applications such as tracking and commerce. The information on these chips is also capable of being remotely accessed without the owner's knowledge or consent.
There is a strong interest to protect RFID enabled cards, tags and devices from snooping. Currently, some physical shielding means for RFID and contactless smart cards consist of a container that enclose all sides of the device (Faraday cage) through use of a conductive material such as a metal to prevent RF signals from entering or escaping the inside of the shield. For example, Cord Technologies developed a product called SMARTSHIELD that completely encloses the smartcard and is made from a high-nickel content metal alloy that can shield the contactless card from magnetic fields. Likewise, U.S. Pat. No. 6,121,544 issued to Petsinger (2000) describes a shield that uses a sheet of magnetic shielding material shaped to substantially surround the contactless smartcard with sufficient thickness to reduce the magnetic field strength inside the shield to below the threshold required to power the smartcard.
Magnetically shielded card holders do currently exist for magnetic strip cards but the purpose of these shields is to protect the data stored on the magnetic strip from stray magnetic fields (such as from televisions and speakers) that can inadvertently damage the magnetic strip. See for example, U.S. Pat. No. 4,647,714 issued to Goto (1987) or U.S. Pat. No. 5,288,942 issued to Godry and Westfield (1994). Likewise, other shields that currently exist are designed to shield the chip from the effects of electrostatic potential accumulations and discharges while being receptive to magnetic fields. See for example U.S. Pat. No. 5,360,941 issued to Roes (1994). Additionally, neither of these types of shields allows control over when a data exchange takes place between the card or tag and the reader.